The present invention relates to a composition of nanoplates and nanotubes wherein at least a portion of the nanoplates have at least one nanotube interspersed between two nanoplates. In particular, is described the exfoliation and dispersion of carbon nanotubes and graphene structures resulting in high aspect ratio, surface-modified carbon nanotube/graphene compositions that are readily dispersed in various media. Graphene structures here is meant to include graphene and oxygenated graphene structures. The carbon nanotubes here is meant to include carbon nanotubes and oxidized carbon nanotubes. The oxygenated structures of carbon nanotubes or graphene include, but are not limited to, carboxylic acid, amide, glycidyl and hydroxyl groups attached to the carbon surface.
These nanoplate-nanotube mixtures can be further modified by surface active or modifying agents. This invention also relates to nanoplate-nanotube composites with materials such as elastomers, thermosets, thermoplastics, ceramics and electroactive or photoactive materials. The graphene-carbon nanotube compositions are also useful as catalysts for chemical reactions. Also, the present invention pertains to methods for production of such composites in high yield.
Carbon nanotubes in their solid state are currently produced as agglomerated nanotube bundles in a mixture of chiral or non-chiral forms. Various methods have been developed to debundle or disentangle carbon nanotubes in solution. For example, carbon nanotubes may be shortened extensively by aggressive oxidative means and then dispersed as individual nanotubes in dilute solution. These tubes have low aspect ratios not suitable for high strength composite materials. Carbon nanotubes may also be dispersed in very dilute solution as individuals by sonication in the presence of a surfactant. Illustrative surfactants used for dispersing carbon nanotubes in solution include, for example, sodium dodecyl sulfate and PLURONICS. In some instances, solutions of individualized carbon nanotubes may be prepared from polymer-wrapped carbon nanotubes. Individualized single-wall carbon nanotube solutions have also been prepared in very dilute solutions using polysaccharides, polypeptides, water-soluble polymers, nucleic acids, DNA, polynucleotides, polyimides, and polyvinylpyrrolidone. The dilution ranges are often in the mg/liter ranges and not suitable for commercial usage.
If graphene is exfoliated, i.e., with the individual plates separated rather than stacked, in medium such as water, the thermodynamic energies due to incompatibility and the very high surface area of the graphene results in the plates recombining, and the plates become very difficult to separate into individual plates. Likewise, if graphene plates are to be oxidized, if the plates are bundled, then only the edges of the graphene are readily accessible for reaction.
In the present invention, discrete tubes ranging in diameter from a nanometer to 100 nanometers can be inserted between inorganic plates. In particular, carbon nanotubes can be inserted between graphene plates thus restricting their agglomeration and facilitating exfoliation in a broad range of materials including liquids and solids. Furthermore, as the plates are now separated, reactions can be entertained at the surface of the graphene plates to give, for example, oxygenated graphene structures. The diameter of the tubes can be used to control the inter plate distance. Selecting tubes of different diameters can lead to controlled transport of molecules or ions between the plates.
In view of the foregoing, nanoplate-discrete nanotube compositions and methods for obtaining them are of considerable interest in the art. A number of uses for discrete nanotube/single inorganic plates, particularly carbon nanotube/graphene compositions, are proposed including, for example, energy storage devices (e.g., ultracapacitors, supercapacitors and batteries), field emitters, conductive films, conductive wires, photoactive materials, drug delivery and membrane filters. Use of discrete carbon nanotube/graphene compositions as a reinforcing agent in material composites is another area which is predicted to have significant utility. Materials include, for example, polymers, ceramics, rubbers, cements. Applications include tires, adhesives, and engineered structures such as windblades, aircraft and the like.
One embodiment of this invention includes a composition comprising inorganic plates with individual plate thickness less than 10 nanometers, termed nanoplates, interspersed with at least a portion of discrete nanotubes of diameter ranging from about 1 nanometer to 150 nanometers and aspect ratio about 10 to 500. Preferably the inorganic plates are graphene and the discrete nanotubes are carbon nanotubes. The range of weight ratio of inorganic plates to nanotubes is about 1:100 to 100:1. The mixture of nanoplates and nanotubes may further comprise a polymer selected from the group consisting of thermoplastics, thermosets and elastomers and/or inorganic materials selected from the group consisting of ceramics, clays, silicates, metal complexes and salts.
A further embodiment of this invention includes a mixture of nanoplates and nanotubes which may further comprise at least one electroactive material, which may be useful, for example, in an energy storage device or photovoltaic.
A yet further embodiment of this invention is a composition of nanoplates and nanotubes further comprising at least one transition metal complex or active catalyst species. An active catalyst can be ionically, or covalently attached to the discrete nanotubes, or inorganic plates or combinations thereof. The chemical reactions can involve contact of the composition with, for example, but not limited to, alkenes and alkynes, chemical moieties containing oxygen, chemical moieties containing nitrogen, chemical moieties containing halogen, and chemical moieties containing phosphorous. The composition may be in the form of a powder for gas phase reaction or in the form of a liquid mixture for solution and slurry phase reactions.
Another embodiment of this invention is a method for preparing graphene carbon nanotube composites, said method comprising: a) suspending non-discrete graphene and non-discrete carbon nanotube fibers in an acidic solution for a time period; b) optionally agitating said suspension; c) sonically treating said suspension of graphene-carbon nanotubes to form graphene-discrete carbon nanotube fibers; and d) isolating the resultant graphene-discrete carbon nanotube composition from the acid prior to further treatment using solid/liquid separations, wherein said separations comprise filtration.
Another embodiment of this invention is a method for preparing inorganic plate-carbon nanotube composites, said method comprising: a) suspending non-discrete carbon nanotube fibers in an acidic solution for a time period, b) sonically treating said suspension of carbon nanotubes to form discrete carbon nanotube fibers, c) isolating the resultant oxidized discrete carbon nanotube composition from the acid, d) washing the oxidized discrete carbon nanotubes with water or other liquids to remove acid, e) redispersing the discrete oxidized carbon nanotubes with inorganic plates, optionally with surfactants and sonication, f) optionally adding a polymer, g) optionally adding a transition metal complex, h) optionally adding an electroactive material, i) optionally adding a ceramic, j) separating the mixture and optionally drying.
A further embodiment of this invention is the composition nanoplates and nanotubes in the form of a part of a fabricated article such as a tire, industrial rubber part or wind blade. The compositions are also useful for batteries, capacitors, photovoltaics catalysts and catalyst supports. Further utility is envisioned, but not limited to, membranes, conductive inks, sensors and static management and electromagnetic shielding.